Peptides and Proteins - SS3 Chemistry Lesson Note
Peptides and proteins are essential biomolecules that play crucial roles in various biological processes. They are composed of amino acids linked together by peptide bonds, forming polypeptide chains. The distinction between peptides and proteins lies in their size, with peptides being smaller than proteins. Understanding the properties and functions of peptides and proteins is essential for comprehending the complexities of life processes. Let's explore peptides and proteins in detail:
Peptides:
Peptides are short chains of amino acids, typically containing fewer than 50 amino acid residues. They are formed through the condensation reaction between the carboxyl group of one amino acid and the amino group of another, resulting in the formation of a peptide bond (CO-NH). Peptides can be classified into several categories based on their length:
1. Dipeptides: Dipeptides consist of two amino acid residues linked by a single peptide bond.
2. Tripeptides: Tripeptides have three amino acid residues and two peptide bonds.
3. Oligopeptides: Oligopeptides contain several (usually less than 20) amino acid residues.
4. Polypeptides: Polypeptides are larger chains of amino acids, often containing up to 50 amino acid residues. When the chain exceeds 50 residues, it is usually considered a protein.
Peptides have diverse biological functions, including hormone regulation, enzymatic activity, and cell signalling. Examples of important peptides include oxytocin, vasopressin, and many neuropeptides that act as neurotransmitters in the nervous system.
Proteins:
Proteins are large biomolecules composed of one or more polypeptide chains folded into specific three-dimensional structures. Proteins are crucial for the structure, function, and regulation of cells and are involved in nearly all cellular processes. They can be classified into several categories based on their structure and function:
1. Fibrous Proteins: Fibrous proteins have elongated shapes and are often involved in structural roles. Examples include collagen, which provides structural support to connective tissues, and keratin, which forms hair, nails, and the outer layer of skin.
2. Globular Proteins: Globular proteins have compact, spherical shapes and are typically involved in enzymatic functions, transport, and regulation. Examples include enzymes like amylase, transport proteins like haemoglobin, and regulatory proteins like insulin.
3. Membrane Proteins: Membrane proteins are embedded in cell membranes and play essential roles in cell signalling, transport of molecules across membranes, and cell adhesion.
Protein Structure:
Proteins have a hierarchical structure:
1. Primary Structure: The sequence of amino acids in the polypeptide chain is referred to as the primary structure. The specific sequence determines the protein's unique properties and functions.
2. Secondary Structure: The secondary structure refers to local folding patterns within the polypeptide chain, including α-helices and β-sheets. These structures are stabilised by hydrogen bonds between the peptide backbone atoms.
3. Tertiary Structure: The tertiary structure is the overall three-dimensional arrangement of the polypeptide chain, including interactions between side chains. It is critical for the protein's stability and function.
4. Quaternary Structure: Some proteins are composed of multiple polypeptide subunits arranged in a specific manner, known as the quaternary structure. These subunits can be identical or different and interact through non-covalent bonds.
Protein Functions:
Proteins perform a wide range of functions in living organisms, including:
● Enzymes: Catalyse biochemical reactions.
● Structural Proteins: Provide support and maintain cell shape.
● Transport Proteins: Carry molecules across cell membranes or throughout the body.
● Hormones: Act as chemical messengers, regulating various physiological processes.
● Antibodies: Play a role in the immune response, defending against foreign invaders.
● Receptors: Bind to specific molecules, initiating signalling pathways within cells.
Overall, peptides and proteins are critical components of life, with diverse functions that are essential for maintaining the structure, function, and regulation of living organisms. Understanding their structures and roles is fundamental in fields such as biochemistry, molecular biology, medicine, and biotechnology.